qt: Add missing #include <functional>

* lang/qt/src/qgpgmenewcryptoconfig.cpp,
lang/qt/src/threadedjobmixin.h: Include functional.

--
With GCC 7.0, functional is not included transitively and we get:
In file included from qgpgmedeletejob.h:39:0,
                 from qgpgmedeletejob.cpp:38:
threadedjobmixin.h:98:33: error: 'function' in namespace 'std'
    does not name a template type
     void setFunction(const std::function<T_result()> &function)
                                 ^~~~~~~~

std::{function,bind,placeholders,mem_fn} are defined in functional.

References: https://bugzilla.redhat.com/show_bug.cgi?id=1417383
Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

GnuPG-Bug-Id: 2955

Commit Message amended by Andre Heinecke

Signed-off-by: Andre Heinecke <aheinecke@intevation.de>

lang/qt/src/qgpgmenewcryptoconfig.cpp

@@ -49,6 +49,7 @@
 #include <sstream>
 #include <string>
 #include <cassert>
+#include <functional>
 
 using namespace QGpgME;
 using namespace GpgME;

lang/qt/src/threadedjobmixin.h

@@ -51,6 +51,7 @@
 #include "job.h"
 
 #include <cassert>
+#include <functional>
 
 namespace QGpgME
 {